The present invention relates to intraocular lenses and more particularly to improved haptics for intraocular lenses.
Intraocular lenses are employed as replacements for the crystalline lens after either extracapsular or intracapsular surgery for the removal of a cataract. Intraocular lenses are generally of two types, those that are placed in the anterior chamber, i.e., between the iris and the cornea, and those that are placed in the posterior chamber, i.e., behind the iris. Both types of lenses are conventionally employed with a choice between an anterior and a posterior lens being partly dictated by the requirements of the patient and partly dictated by the choice of the physician inserting the lens.
Intraocular lenses normally consist of an optic with two or more haptics that extend generally radially from the optic and include a foot portion that normally seats in the scleral spur for an anterior lens and either in the ciliary sulcus or within the lens capsule for a posterior lens. The optic normally comprises a circular transparent optical lens. The haptic in most lenses is a flexible fiber or filament having at least one end affixed to the lens and having a second portion extending generally radially away from the lens to form a seating foot. Several haptic designs are currently in use, for example, U-shaped loops in which both ends of each loop are connected to the lens and J-shaped loops in which only one end of the loop is affixed to the lens. Generally, when U-shaped or J-shaped haptics are employed, two such haptics are utilized with each lens. The haptics are generally diametrically positioned about the optic.
While the haptics are flexible so that they can be compressed radially inwardly during insertion and so that they exert a slight amount of force on the portion of the eye on which they seat to center the lens on the optical axis of the eye, the force required to compress the haptics radially inwardly increases with increasing compression distance. If the force exerted on the eye exceeds a comfortable level, it can at times cause irritation to the eye. For example, a typical lens constructed in accordance with prior art techniques exhibits a compression force when the haptics are compressed a combined distance of 1.5 millimeters of about 2.0 grams. When the haptics are only slightly compressed, the resistive force exerted by the haptics is much smaller.
This characteristic presents difficulty with respect to the proper and comfortable fitting of a lens in the eyes of various patients which, of course, vary significantly in size. Since it is desirable for the compression force exerted by the haptics to be on the order of 1 gram or less, it has become necessary to vary the diameter of the optic as well as the distance from the optical axis at which the seating foot of the haptic resides when relaxed, in order to minimize the force the haptics exert on eye tissue. This results in the necessity to maintain large inventories of lenses of various sizes in order to have the appropriate lens available at the time of surgery.
Moreover, some prior art haptic designs employ what is referred to as four point contact, again generally using two haptics, each of which have two seating portions that are spaced circumferentially relative to the optic. Using this design, the seating pressure on the eye can be spread over a greater distance thus reducing eye irritation or tenderness. Problems have been encountered with four point contact type lens in achieving equal resistive forces at each of the contact locations.